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<body>
<div class="document" id="pyspec-design-by-contract-guide">
<h1 class="title">PySpec Design by Contract Guide</h1>
<table class="docinfo" frame="void" rules="none">
<col class="docinfo-name" />
<col class="docinfo-content" />
<tbody valign="top">
<tr><th class="docinfo-name">Author:</th>
<td>Shibukawa Yoshiki</td></tr>
<tr><th class="docinfo-name">Contact:</th>
<td>yoshiki at shibu.jp</td></tr>
<tr><th class="docinfo-name">Copyright:</th>
<td>This document has been placed in the public domain.</td></tr>
</tbody>
</table>
<div class="contents topic">
<p class="topic-title first"><a id="contents" name="contents">Contents</a></p>
<ul class="simple">
<li><a class="reference" href="#how-to-write-dbc-verification-methods" id="id1" name="id1">How to write DbC verification methods</a><ul>
<li><a class="reference" href="#verifying-methods" id="id2" name="id2">Verifying Methods</a></li>
</ul>
</li>
<li><a class="reference" href="#how-to-run-with-design-by-contract" id="id3" name="id3">How to Run with Design by Contract</a><ul>
<li><a class="reference" href="#run-on-pyspec" id="id4" name="id4">Run on PySpec</a></li>
<li><a class="reference" href="#run-on-your-own-application" id="id5" name="id5">Run on Your Own Application</a></li>
</ul>
</li>
</ul>
</div>
<p><em>This feature was born recently. I don't use it enough.</em></p>
<p>Design by Contract(DbC) comes from Eiffle. xUnit tests over interface.
DbC tests from more internal side than xUnit(I think).</p>
<p>PySpec supports Design by Contract. You can write any condition checkers
into your application.</p>
<p>This sample file is <tt class="docutils literal"><span class="pre">pyspec/sample/sample_dbc.py</span></tt>.</p>
<div class="section">
<h1><a class="toc-backref" href="#id1" id="how-to-write-dbc-verification-methods" name="how-to-write-dbc-verification-methods">How to write DbC verification methods</a></h1>
<p>The class that supports Design by Contract feature should have <tt class="docutils literal"><span class="pre">DbCobject</span></tt>
base class, and call base class's <tt class="docutils literal"><span class="pre">__init__()</span></tt> methods.</p>
<p>sample:</p>
<pre class="literal-block">
from pyspec.embedded import *
from pyspec.embedded.dbc import DbCobject, DbC

class Weight(DbCobject):
    convert_table = {&quot;kg&quot;:1.0, &quot;kan&quot;:3.75, &quot;pound&quot;:0.45359237}

    def __init__(self, unit, value):
        super(Weight, self).__init__()
        self.set_unit(unit)
        self.value = value

    &#64;DbC
    def set_unit__pre(self, unit):
        About(unit in self.convert_table).should_be_true()

    def set_unit(self, unit):
        self.unit = unit
</pre>
<div class="section">
<h2><a class="toc-backref" href="#id2" id="verifying-methods" name="verifying-methods">Verifying Methods</a></h2>
<p>If you have created methods that have following naming rule, PySpec would
call these methods. And these methods should be decorated by &#64;DbC.</p>
<table border="1" class="docutils">
<colgroup>
<col width="21%" />
<col width="79%" />
</colgroup>
<thead valign="bottom">
<tr><th class="head">Naming Rule</th>
<th class="head">Description</th>
</tr>
</thead>
<tbody valign="top">
<tr><td><tt class="docutils literal"><span class="pre">XXX__pre</span></tt></td>
<td>This method was called before the XXX method is called.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">XXX__post</span></tt></td>
<td>This method was called after the XXX method is called.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">__invariant</span></tt></td>
<td>This method was called after all methods are called.</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section">
<h1><a class="toc-backref" href="#id3" id="how-to-run-with-design-by-contract" name="how-to-run-with-design-by-contract">How to Run with Design by Contract</a></h1>
<p>There are two ways to run DbC.</p>
<div class="section">
<h2><a class="toc-backref" href="#id4" id="run-on-pyspec" name="run-on-pyspec">Run on PySpec</a></h2>
<p>You have to do nothing.</p>
</div>
<div class="section">
<h2><a class="toc-backref" href="#id5" id="run-on-your-own-application" name="run-on-your-own-application">Run on Your Own Application</a></h2>
<p>At first, you should call <tt class="docutils literal"><span class="pre">pyspec.embedded.dbc.set_dbc_option()</span></tt>.</p>
<table border="1" class="docutils">
<colgroup>
<col width="20%" />
<col width="80%" />
</colgroup>
<thead valign="bottom">
<tr><th class="head">Option</th>
<th class="head">Description</th>
</tr>
</thead>
<tbody valign="top">
<tr><td><tt class="docutils literal"><span class="pre">prepost</span></tt></td>
<td>Enable <tt class="docutils literal"><span class="pre">XXX__pre</span></tt> and <tt class="docutils literal"><span class="pre">XXX__post</span></tt> (default=False)</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">invariant</span></tt></td>
<td>Enable <tt class="docutils literal"><span class="pre">__invariant</span></tt> (default=False)</td>
</tr>
</tbody>
</table>
<p>example:</p>
<pre class="literal-block">
pyspec.embedded.dbc.set_dbc_option(prepost=True, invariant=True)
</pre>
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